In the medical field blood comes primarily into consideration as a sample. In the following reference is made to blood analysis as an example without limiting the generality.
A particularly important field of application in blood analysis is monitoring the blood sugar level of diabetics which is frequently used especially in the analytical field of blood sugar self-monitoring (home monitoring).
Photometric, carrier-bound tests are widely used in this field of application. Such test elements are often used as single-use articles which usually contain a reagent system that reacts irreversibly with an analyte of a sample and results in a characteristic, optically measurable change of the test element.
Conventional test elements that are used for photometric tests are usually in the form of test strips known in the prior art on which a test field is mounted. The test field consists of a reagent system which can fulfil different functions. The sample is applied to the upper side of the test field. After the required reaction time has lapsed, characteristic colour changes are measured by reflection photometry with the aid of an analytical unit in order to analyse the sample. The evaluation device which is provided to evaluate an analytical result, is usually suitable for a very particular type of test elements of a particular manufacturer. The test elements and the evaluation instrument thus form mutually harmonized components and are usually referred to overall as an analytical system. Such analytical systems are described for example in U.S. Pat. Nos. 5,281,395 and 5,424,035, the disclosures of which are each hereby incorporated by reference.
Lancing devices which can be used by the patient to make an opening in the skin are provided in addition to the analytical systems in order to draw a blood sample especially in the home monitoring field. The blood which flows out through the skin opening can be applied to a test element. The described system requires a complex handling by the user in which he must firstly make a wound in order to have a sufficient sample volume for the blood analysis. The site at which the blood emerges is subsequently contacted with the test field of a test element so that sufficient sample can penetrate into the test field. Afterwards the test field containing the sample has to be positioned relative to an analytical unit in order to analyse the test field.
In order to simplify the described complex process for the user, systems are offered in the prior art which combine several working steps.
A blood collecting system is described in the document WO 97/42888 which can be used on the one hand to make a wound in a part of the body so that blood emerges from the body opening for analysis. On the other hand, the blood collecting system is also designed such that a cannula in the system which is arranged near to the lancet and thus near to the site of incision is suitable for taking up blood. Hence the sample can be sucked into the cannula after the lancing process by means of capillary effects and subsequently be delivered onto a test element provided for this purpose containing a reagent system. The test elements used for this are designed in a manner well known in the prior art and are used accordingly. Although the described system simplifies sample application on the test element for the user, separate operating steps are required by the user to transfer the blood from the cannula onto a test field.
The document U.S. Pat. No. 4,360,016 discloses a blood collecting system. In addition to the aforementioned handling steps, the described prior art is also disadvantageous because an increased amount of sample is required in the system. After the sample has been collected and delivered through a cannula, an adequate sample volume must also be available for application to the test field.
An analytical system is also described in the U.S. Pat. No. 4,627,445. For this a skin opening from which blood can emerge is firstly made with a lancet. Due to the prevailing underpressure in the system, the blood is sucked into the analytical system from the blood discharge site through a lateral channel and is passed to a test field. The test field is arranged in the analytical system in such a manner that a measuring unit which is positioned directly above the test field can analyse the test field.
A disadvantage of the described prior art is the very complex design of the analytical system which, among others, requires an underpressure for sample collection. Furthermore, a sufficient volume of sample must emerge from the body opening in order to completely cover the test field after the sample has been conveyed in the transport channel to the test field.
In order to have a sufficient amount of sample for such systems despite the given dead volumes in the transport channels, the piercing depth of the lancet must in principle be correspondingly deep and thus a sufficiently large wound must be selected. However, an increased puncture depth results in increased pain sensation which should be avoided especially in the case of patients who have to draw blood several times daily.